The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
The human retina has a static dynamic range of approximately 100:1. This means that the darkest area in a field of view that can be distinguished by the retina is 1/100th as bright as the brightest area in the field of view that can be distinguished. But as the eye moves around in a scene to focus on new objects, the retina adjusts its exposure both chemically and geometrically (by adjusting the iris size of the pupil) in order to adjust to brighter and darker objects in an environment. This exposure adjustment occurs so quickly that a person does not notice it happening. The result is that the human eye has an effective dynamic range of 1,000,000:1, allowing a person to perceive both dark and bright objects in a high dynamic range (HDR) environment.
A typical 8-bit digital camera, on the other hand, can produce images having a dynamic range of 255:1, and a typical liquid crystal (LCD) display or cathode ray tube (CRT) display has a dynamic range of approximately 200:1. Thus, digital photographs and typical display devices have dynamic ranges that are far less than the effective dynamic range of the human eye. And when a person views an HDR image, they are often frustrated to see that the photograph shows neither the bright objects nor the dark objects very well, even though they can easily perceive both types of objects when using their own eyes to view the same scene. A typical example is a photograph of a person standing indoors next to a window. Even though the person standing next to the window can be easily seen with the naked eye, a photograph of the scene makes the person too dark to perceive.
To resolve this issue, tone curves are often applied to HDR images. Tone curves adjust the brightness of the pixels in the image to make the dark objects brighter and the bright objects darker. Another solution is to increase the backlighting of the image being displayed in order to more easily see features in dark regions.